Interpreting Tan Delta test results

[dman504]

So we just had some tan delta testing done on a couple of existing cables. For each of the cables, the "A" phase started off with very high TD values (12) and as testing progressed from 7kVrms to 23kVrms the values diminished to about 2. I would have expected the lines to either be fairly level or go up as voltage levels increased. The "B" and C"C phases were fairly level. Anyone have an explanation for this?

 

[Phil Corso]

Dman...

Can you provide additional data:

1) 3 x 1-core cables?

2) 1 x 3 Core?

3) Voltage rating?

4) Current rating?

5) Size?

6) Shielded? What mat'l?

7) Jacketed? What mat'l?

8) Insulation?

9) Cable length?

10) All phases tested at about the same time?

11) Ambient temp at time of test?

12) Were cables "dried-out" before test!

13) Age?

Regards, Phil Corso

 

[GoldDigger]

I had to look up Tan Delta, and found some good stuff at http://www.hvinc.com/downloads/Tan_Delta_FAQ.pdf

The only reason that I can think of right off hand would be that since you did the lower voltage measurements first, the cable was drying out during the testing period.

 

[Bugman1400]

I had to look up Tan Delta, and found some good stuff at http://www.hvinc.com/downloads/Tan_Delta_FAQ.pdf

The only reason that I can think of right off hand would be that since you did the lower voltage measurements first, the cable was drying out during the testing period.

LOL, I also had to look this up and I've been HI-potting and meggaring cables for years. This sounds like junk science to me. To me cables are like bearings, they can test good and then fail at anytime soon after they are placed in-service. For me to be convinced in this technology, I would have to read an IEEE paper or from some other professional entity that is not sponsored by the manufacturer of the test equipment.

Just my 2 cents.

 

[dman504]

Dman...

Can you provide additional data:

1) 3 x 1-core cables?

2) 1 x 3 Core? (3 conductor Teck)

3) Voltage rating? (25kV)

4) Current rating? (500MCM)

5) Size? (500MCM)

6) Shielded? What mat'l? (Shielded copper ribbon)

7) Jacketed? What mat'l? (Inner jacket PVC)

8) Insulation? (XLPE) 100%

9) Cable length? (410 meters)

10) All phases tested at about the same time? (A-first then B then C about 40 min between)

11) Ambient temp at time of test? ( 70 degrees)

12) Were cables "dried-out" before test! (cables were in service before test and assumed to be dry)

13) Age? (6 years)

Regards, Phil Corso

Hi Phil, sorry for late reply,
Please see responses in ( )

 

[dman504]

LOL, I also had to look this up and I've been HI-potting and meggaring cables for years. This sounds like junk science to me. To me cables are like bearings, they can test good and then fail at anytime soon after they are placed in-service. For me to be convinced in this technology, I would have to read an IEEE paper or from some other professional entity that is not sponsored by the manufacturer of the test equipment.

Just my 2 cents.

I think it is a little bit on the witchcraft side myself however many clients are asking for it lately. Thanks for your input.

 

[dman504]

I had to look up Tan Delta, and found some good stuff at http://www.hvinc.com/downloads/Tan_Delta_FAQ.pdf

The only reason that I can think of right off hand would be that since you did the lower voltage measurements first, the cable was drying out during the testing period.

The cable was in service just prior to the test and local weather was not humid. It is however a buried cable and moisture ingress is not impossible. It did pass the VLF and has since been put back into service, just trying to gain some validity for the Tan Delta. Thanks for your time.

 

[Phil Corso]

DMan?

There is no doubt that Tan-Delta testing of cable is overkill. It was original developed to detect slot-insulation failure in xfmrs and rotating equipment!

Your test is significant in that 2-phases seem to track OK, but the 3^rd is very unusual. This suggests an error or omission in test procedure during test (You probably figured out that Tan-Delta is not as simple as other ?cable? testing methods!) And, of course there was no further testing !

Re Bugman?s comment, ?? they can test good and then fail at anytime soon after they are placed in-service? ! It?s far worse when an insulation test goes awry during the test? on a far-away island?

Regards, Phil